This invention relates generally to the field of additive manufacturing. In particular the invention relates to turbine components with bimodal radial grain size distributions.
In gas turbine engines, disks which support turbine blades rotate at high speeds in a high temperature environment. In modern engines, operating temperatures can exceed 1500° F. (816° C.) in the exterior or rim portion of disks, and about 1000° F. (538° C.) at the inner or hub portions. In addition to this radial temperature gradient, there is also a stress gradient, with higher stresses occurring in the lower temperature hub region, while lower stresses occur in the higher temperature rim region in a typical disk. These differences in operating conditions radially across a disk result in different mechanical property requirements in the different disk regions, with the rim portion subjected to severe creep and hold time fatigue crack growth conditions, and the hub portion subjected to severe fatigue and high stress conditions. In order to achieve the maximum operating conditions in terms of efficiency and performance in an advanced turbine engine, it is desirable to utilize disk alloys having excellent hold time fatigue crack growth resistance and high temperature creep resistance in the rim portion while having high tensile strength and fatigue crack resistance at moderate temperatures in the hub portion.